Biphenols are very useful chemicals. Biphenol itself can be used in the manufacture of polyesters and polyurethanes. Ethanox.RTM.712 Antioxidant (a product of Ethyl Corporation) is the compound 4,4'-bis(2,6-di-tert-butylphenol) and is a very effective antioxidant especially in polymer compositions.
A number of procedures for making biphenols have been reported. Zaweski, U.S. Pat. No. 3,562,338, describes a process for making 4,4'-bis(2,6-di-substituted phenols) by the air oxidation of one mole of 2,6-di-substituted phenol to the corresponding diphenoquinone using an alkali metal hydroxide catalyst followed by reaction with an additional one mole of 2,6-di-substituted phenol in the absence of oxygen to form a 4,4'-bis(2,-6-di-substituted phenol) by an oxidation-reduction reaction.
Zaweski U.S. Pat. No. 3,562,338 also describes a process in which a 2,6-di-alkylphenol is oxidized with air in the presence of a base until one-half of the phenol is converted to the corresponding diphenoquinone. The remaining phenol is unchanged. Air is discontinued and the mixture is heated to convert the entire reaction mixture to 4,4'-bis(2,6-di-alklyphenol).
Hay U.S. Pat. No. 3,631,208 is similar to Zaweski but prefers trimethylamine, heterocyclic amines, metal alkoxides, metal phenoxides or carboxylic acids as the oxidation catalyst.
Reichle U.S. Pat. No. 4,238,627 describes a process similar to that of Zaweski in which the amount of air used to oxidize the 2,6-dialkylphenol is limited to the stoichiometric amount required to convert the phenol to a biphenol.
Strom U.S. Pat. No. 4,410,736 is a modification of the Hay process conducted in a lower alkanol.
Kirshner U.S. Pat. No. 4,447,656 describes a process of catalytically dehydrogenating 2,6-di-tert-butylphenol to the corresponding 4,4'-diphenoquinone and then hydrogenating the diphenoquinone to a 4,4'-biphenol.
Strom U.S. Pat. No. 4,482,754 describes a continuous process of converting 2,6-dialkylphenols to biphenols by reaction with oxygen in the presence of an oxidation catalyst to form the corresponding diphenoquinone followed by reaction with more 2,6-dialkylphenol to form a biphenol.
Makato et al. U.S. Pat. No. 4,564,713 teach a process of dimerizing alkylphenols in an aqueous system containing a surfactant using a copper compound and a basic boron compound as a catalyst.